Assistant U.S. Attorney Jean Piccone is a federal prosecutor and a friend of A.D.A. Jack McCoy. Her husband was murdered due to her crusade against the Masucci Crime Family.
In spite of the hitman responsible, Cary Stillman, being arrested and agreeing to turn on his employer, Federico Righetti, the FBI made Stillman take the full sentence just to get Federico released and their case against him could build to tie him to his affiliates. It instead ended up in his nephew Peter killing Federico. (L&O: "Payback")